Conventional percussion primer mixes of almost all calibers of small arms ammunition traditionally utilized, for the most part, a combination of lead styphnate as the initiating explosive, antimony sulfide as the fuel, and barium nitrate as the oxidizer in various ratios. Besides these lead, antimony and barium containing compounds, various other compounds containing objectionable chemicals such as mercury, potassium chlorate, and like have also been used in percussion primers in various ratios. Due to the toxicity, ecological impact, corrosiveness, and/or expensive handling procedures during both production and disposal of such objectionable chemicals, there has been an effort to replace compounds containing such objectionable chemicals in percussion primers.
The Department of Defense (DOD) and the Department of Energy (DOE) have made a significant effort to find replacements for toxic metal based percussion primers. Furthermore, firing ranges and other locales of firearms usage have severely limited the use of percussion primers containing toxic metal compounds due to the potential health and handling risks associated with the use of lead, barium and antimony.
Ignition devices have traditionally relied on the sensitivity of the primary explosive, which significantly limits available primary explosives. The most common alternative to lead styphnate is diazodinitrophenol (DDNP). DDNP-based primers, however, do not fully meet commercial or military reliability and have been for several decades relegated to training ammunition, as such primers suffer from poor reliability that may be attributed to low friction sensitivity, low flame temperature, and are hygroscopic. The ability of a percussion primer to function reliably at low temperatures becomes particularly important when percussion primed ammunition is used in severe cold, such as in aircraft gun systems that are routinely exposed to severe cold.
Another potential substitute for lead styphnate that has been identified is metastable interstitial composites (MIC) (also known as metastable nanoenergetic composites (MNC), nano-thermites or superthermites), which includes Al—MoO3, Al—WO3, Al—CuO and Al—Bi22O3. In these composites, both the aluminum powder and oxidizing material have a particle size of less than 0.1 micron and more preferably between 20-50 nanometers. The thermite interaction between the fuel and oxidizer resulting from high surface area and minimal oxide layer on the fuel has resulted in excellent performance characteristics, such as impact sensitivity, high temperature output, and reliability under stated conditions (−65° F. to +160° F.). However, it has been found that these systems, despite their excellent performance characteristics, are difficult to process safely and cost-effectively on a large-scale. The main difficulty is handling of nano-size powder mixtures due to their sensitivity to friction and electrostatic discharge (ESD), and their reactivity in air. See U.S. Pat. No. 5,717,159 and U.S. Patent Publication No. 2006/0113014. As a result, much technology has been devoted to the safe and cost-effective handling of these nano-sized materials.
Still another potential substitute for lead styphnate that has been identified are compounds that contain moderately insensitive explosives that are sensitized by nano-sized fuel particles. The explosive in such compounds is moderately insensitive to shock, friction and heat according to industry standards and has been categorized generally as a secondary explosive due to their relative insensitivity. Examples of such energetics include CL-20, PETN, RDX, HMX, nitrocellulose and mixtures thereof. The nano-sized fuel particles have an average particle size less than about 1500 nanometers and most suitably less than 650 nanometers, which may include aluminum, boron, molybdenum, silicon, titanium, tungsten, magnesium, melamine, zirconium, calcium silicide or mixtures thereof. See, for example, U.S. Patent Publication No. 2006/0219341 and U.S. Patent Publication No. 2008/0245252. However, safety and cost-efficiency concerns still remain due to the nano-size fuel particles, despite such compounds exhibiting excellent performance characteristics.
In light of the foregoing identified problems, there remains a need in the art for a percussion primer that is free of toxic metals, is non-corrosive and non-erosive, may be processed and handled safely and economically, has superior sensitivity and ignition performance characteristics compared to traditional primer mixes, contains non-hydroscopic properties, is stable over a broad range of storage conditions and temperatures, and is cheaper to produce than conventional heavy metal primer mixes.